Sub-pixel regions on the faceplate of a flat panel display are typically separated by an opaque mesh-like structure commonly referred to as a "black matrix". By separating sub-pixel regions, the black matrix prevents electrons directed at one sub-pixel from being "back-scattered" and striking another sub-pixel. In so doing, a conventional black matrix helps maintain sharp resolution in a flat panel display. In addition, the black matrix is also used as a base on which to locate structures such as, for example, support walls.
In one prior art black matrix, a very thin layer (e.g. approximately 2-3 microns) of a conductive material is applied to the interior surface of the faceplate surrounding the sub-pixel regions. Typically, the conductive black matrix is formed of a conductive graphite material. By having a conductive black matrix, excess charges induced by electrons striking the top or sides of the black matrix can be easily drained from the interior surface of the faceplate. As an additional benefit, a conductive black matrix allows one to control the electric potential on the faceplate. Additionally, in a field emission-type flat panel display, by having a conductive black matrix, electrical arcs occurring between field emitters of the flat panel display and the faceplate will be more likely to strike the black matrix. By having the electrical arcing occur between the black matrix and the field emitters instead of between the sub-pixels and the field emitters, the integrity of the phosphors and the overlying aluminum layer is maintained. Unfortunately, due to the relatively low height of such a prior art conductive black matrix, arcing can still occur from the field emitter to the sub-pixel regions. As a result of such arcing, phosphors and the overlying aluminum layer can be damaged. As mentioned above, however, the black matrix is also intended to prevent back-scattering of electrons from one sub-pixel to another sub-pixel. Thus, it is desirable to have a black matrix with a height which sufficiently isolates each sub-pixel from respective neighboring sub-pixels. However, due to the physical property of the conductive graphite material, the height of the black matrix is limited to the aforementioned 2-3 microns.
In another prior art black matrix, a non-conductive polyimide material is patterned across the interior surface of the black matrix. In such a conventional black matrix, the black matrix has a uniform height of approximately 20-40 microns. Thus, the height of such a black matrix is well suited to isolating each sub-pixel from respective neighboring sub-pixels. As a result, such a black matrix configuration effectively prevents unwanted back-scattering of electrons into neighboring sub-pixels. Unfortunately, prior art polyimide black matrices are not conductive. As a result, even though the top edge of the polyimide black matrix is much closer than the sub-pixel region is to the field emitter, unwanted arcing can still occur from the field emitter to the sub-pixel regions. In a prior art attempt to prevent such arcing, a conductive coating (i.e. indium tin oxide (ITO)) is applied to the non-conductive polyimide black matrix. ITO coated non-conductive black matrices are not without problems, however. For example, coating a non-conductive matrix with ITO adds increased complexity and cost to the flat panel display manufacturing process. Also, the high atomic number of ITO components results in unwanted back-scattering of electrons. Furthermore, ITO has an undesirably high secondary electron emission coefficient, .delta..
In yet another approach, (described in a commonly-owned, co-pending U.S. patent application to Drumm, filed Mar. 31, 1997), capillary action is used to define the shape of a black matrix structure. In such an approach, rows and columns of photoresist structures are formed on the surface of the faceplate of the flat panel display device. The photoresist structures are formed on the faceplate directly overlying the areas which are to be used as sub-pixel regions. Conductive material is then applied between the photoresist structures, and is slightly hardened. In this approach, physical properties of the conductive material (e.g. viscosity, surface tension, density, and the like) determine the height and shape of the black matrix structure formed between the rows and columns of the photoresist structures. However, the physical properties of the conductive material may not allow for, or may prevent, the formation of a black matrix structure having particular physical dimensions.
Thus, a need exists for conductive matrix structure having sufficient height to effectively separate neighboring sub-pixels. A further need exists for a conductive matrix structure which reduces arcing from the field emitters to the sub-pixels. Still another need exists for a conductive matrix structure which does not have the increased cost and complexity, the increased back-scattering rate, and the undesirably high secondary electron emission coefficient associated with an ITO-coated black matrix structure. Yet another need exists for a conductive matrix formation method which is not highly dependent upon the physical properties of the material used to form the matrix structure.